The present invention relates generally to methods and apparatus for use in well completion operations, and more particularly relates to methods and apparatus for packing off a well, for placing a seal assembly within a packer, and for actuating apparatus used in well completion operations.
When a packer is set in a well which is to be perforated, it is typically desirable before perforation of the well, to place a seal assembly in the packer bore to facilitate either temporary or permanent production from the well. In many cases, the packer and a perforating mechanism will be run into the well on the end of tubing string. It is also often desirable to utilize an extra long seal assembly to accommodate movement of the tubing string during the life of the well. Conventional technology has required that when a packer was run into the well on the tubing string, if an extra long seal assembly was to be placed in the packer bore, the tubing had to be disconnected from the packer and removed from the well. The extra long seal assembly was then placed on the end of the tubing and run back into the well where it would be stabbed into the packer. This technique presents considerable drawbacks in the removal of the tubing from the well may expend a considerable amount of time and therefore increase the cost of the operation. Additionally, when the tubing is removed from a freely flowing well, the well is normally killed which can lead to formation damage. Other conventional methods for accomodating movement between the tubing and packer are relatively complex and expensive.
The present invention provides a new method and apparatus for running a packer into a well on the end of the tubing string, for setting the packer, and for placing either an extra long seal assembly or another mechanism within the packer bore for accommodating tubing movement, on a single trip with the tubing into the borehole.
Some conventional packer setting techniques include the use of mechanisms which substantially set either an upper or lower packer slip, but require movement of the tubing string to move the packer body in order to set the opposing slip and fully compress the packing element. Such movement of the tubing string is undesirable because it requires movement of a potentially large number of components and requires such components to be subjected to the forces required to set the packer slips.
The present invention also provides a dual-acting packer setting machanism which acts both upon the packer setting sleeve and upon the packer body to fully set the packer without manipulation of the tubing string.
Additionally, many conventional techniques of setting packers and for operating other types of well tools through hydraulic pressure require that the substantial hydraulic pressure needed to set the packer be established in excess of the already existing hydrostatic pressure in the borehole. This substantial increase in pressure, often on the order of 2,500 to 5,000 psi places an undesirable strain on components within the well, as well as upon the well casing itself. Some types of packers and other well tools include integral atmospheric pressure chambers to allow hydrostatic pressure to operate a piston or other movable mechanism. Devices with these integral atmospheric pressure chambers may seize under the hydrostatic pressure in the well or may actuate prematurely. Additionally, because of the time such air chambers may be exposed to the hydrostatic pressure in the well, the air chambers may leak, rendering them inoperative.
The present invention provides a new method and apparatus for setting packers and for operating other types of downhole equipment, such as, for example, tubing releases or firing heads, through use of the pre-existing hydrostatic pressure in the well through placement of a separate chamber of reduced pressure to actuate such packer or other well tool.